Recently, to manufacture electronic components such as semiconductor devices or capacitors, a thin-film coating of paint or the like is fairly often deposited in a pattern on the surface of a band-shaped substrate. For example, it has been suggested for battery electrode plates that an active material layer is formed on the surface of a collector serving as a substrate, and then a porous protective film with a thickness of 0.1 μm to 200 μm or a porous protective film of coating film containing a resin binder and fine particulate solids such as alumina powder is formed to cover the aforementioned active material layer (for example, see Patent Document 1).
The aforementioned porous protective film is applied and deposited intermittently to cover the active material layer that has been applied and deposited in a pattern. To efficiently perform the step of intermittently depositing a coating of paint or the like on a substrate in this manner for volume production, such a step has been employed in which while a substrate shaped like an extra long sheet is traveling at a predetermined speed, paint or the like is intermittently applied and deposited on the substrate (for example, see Patent Document 2). In this intermittent coating method, a rotating coating roll carries a predetermined amount of slurry-state paint using a regulator. The extra long substrate is sandwiched between the coating roll and a backing roll disposed opposite thereto to travel on the backing roll, during which the paint layer on the coating roll is transferred and applied to the substrate. Meanwhile, at predetermined time intervals, the rotation axis of the backing roll is translated in a direction orthogonal to its axial center so that the substrate is spaced apart from the coating roll for a predetermined period of time, thereby forming a non-coating deposited section in which no paint is applied to the substrate.
On the other hand, a die coating scheme has also been conventionally used as another intermittent application means. This die coating method provides control such that paint subjected to pressure and thereby discharged from a die is applied and deposited onto the substrate, and the pressure applied to the paint is interrupted with predetermined timing and slightly reduced at the same time. This ensures that the discharge of the paint from the die is stopped, thereby allowing a thin film coating of paint to be deposited and formed on an intermittent basis.
However, any one of the aforementioned intermittent coating methods is suitable to efficiently deposit and form a coating of thin film relatively as thick as 20 μm or greater, but cannot be employed, due to its configuration, to form a porous protective film with a thickness of 20 μm or less for use such as for battery electrode plates. In contrast to this, there is a gravure coating method available as a technique for depositing a coating of 20 μm or less thin film. The method enables a coating agent to be applied to the entire surface of a thin substrate with very high accuracy and in a uniform thickness with reliability (for example, see Patent Document 3).
As shown in FIG. 9, in the aforementioned gravure coating method, a band-shaped substrate 40 is looped and supported under tension between a pair of freely rotatable attitude control rolls 41 and 42, which are disposed oppositely in parallel to each other, and allowed to travel in a direction orthogonal to the axial directions of both the attitude control rolls 41 and 42. A gravure roll 43, which has a gravure pattern (not shown) formed on its circumferential surface and is disposed below the substrate 40, is rotated at a circumferential velocity having a relative velocity to the substrate 40 while a coating agent is being applied so as to enter the grooves of the aforementioned gravure pattern from a coating agent feed nozzle assembly 44. At the same time, an excess of the coating agent is wiped off the surface of the gravure roll 43 with a doctor blade 47 before the coating agent is applied, thereby allowing a constant amount of the coating agent to be applied to the undersurface of the substrate 40.
In the aforementioned gravure coating method, an excessive amount of the coating agent applied to the grooves of the gravure pattern on the gravure roll 43 is wiped off with the doctor blade 47, thereby allowing an appropriate amount of the coating agent to be supplied into and fill in the grooves of the gravure pattern. In addition to this, since the direction of travel of the substrate 40 is opposite to the direction of rotation of the gravure roll 43 at the contact portion with each other, the gravure pattern slips in a reverse direction on the undersurface of the substrate 40, thereby allowing a thin coating of the coating agent to be uniformly smoothed and deposited on the entire undersurface of the substrate 40. It is thus possible to uniformly apply and form a thin film in a thickness of 20 μm or less.
Incidentally, the aforementioned gravure coating method is suitable to apply a relatively thin film reduced in thickness to 20 μm or less to an entire surface. However, in Patent Document 3, no description is made regarding an intermittent coating technique for intermittently applying coatings to form a thin film while non-coating deposited sections having no coating agent applied thereto are being provided.
A gravure coater of FIG. 9 may be used for intermittently applying coatings, in which included is a roll unit 50 having a travel path of the substrate 40 on a pair of attitude control rolls 41 and 42 and a pair of guide rolls 48 and 49, which are each rotatably disposed. The roll unit 50 is pivoted is about a rotational spindle 51 as the fulcrum to be alternately positioned at the position illustrated with a solid line in the figure and at the position illustrated with a chain double-dashed line. To realize this arrangement, it is contemplated that the substrate 40 is allowed to come into or out of contact with the gravure roll 43, or the entire assembly including the gravure roll 43, the coating agent feed nozzle assembly 44, and a coating agent carrying tank 52 may be configured to move up and down, so that the gravure roll 43 comes into or out of contact with the substrate 40. Alternatively, the attitude control roll 42 may be provided as a stationary reference roll, whereas the rotation axis of the other attitude control roll 41 is moved up and down so that the substrate 40 comes into or out of contact with the gravure roll 43.
However, this method involves an unnecessarily complicated arrangement for allowing the substrate 40 and the gravure roll 43 to come into or out of contact with each other, resulting in its responsivity being significantly reduced. It is thus impossible to apply intermittent coatings of thin film with high productivity. Furthermore, as shown in FIGS. 10A to 10B, the aforementioned bad responsivity during intermittent coating operation causes the substrate 40 and the gravure roll 43 to come into or out of contact with each other with bad stability. Thus, during coating operation, a thin film 53 intermittently applied and formed on the surface of the substrate 40 may be such that a trailing coating edge 53a in the direction of travel P of the substrate 40 is not in an accurate straight line, but becomes wavy along the width of the band-shaped substrate 40 and easily nonuniform in thickness. Such a problem that the trailing coating edge 53a is wavy and nonuniform in thickness in this manner becomes more noticeable particularly when employed is means for moving the other attitude control roll 42 to retreat the substrate 40 towards the backside thereof and advance it towards the frontside thereof, thereby allowing the substrate 40 to come into or out of contact with the gravure roll 43. This is because there occurs slack in the substrate 40 when the attitude control roll 42 is moved to retreat the substrate 40 towards the backside thereof, thereby releasing the pressure exerted on the substrate 40 against the gravure roll 43.
[Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 7-220759
[Patent Document 2] Japanese Patent Laid-Open Publication No. Hei 8-131934
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-179151